Project Summary/Abstract Human papillomavirus (HPV) is a common sexually transmitted infection that causes anal, penile, oropharyngeal cancers in men. Due to their sexual practices, men who have sex with men (MSM) are at particularly high risk for HPV infection and are disproportionately affected by HPV-related cancers. A safe and effective vaccine is available to prevent HPV infection, yet HPV vaccination rates in the U.S. have been low, particularly among males. The Advisory Committee on Immunization Practices (ACIP) recommends HPV vaccination for all MSM through age 26. Nevertheless, recent studies with national samples of gay and bisexual men aged 18-26 indicate that only 13-21% have initiated the 3-dose HPV vaccine series. Our pilot work suggests that many MSM are simply unaware of the vaccine or perceive other important barriers to getting vaccinated. To remedy this gap, the goal of the proposed research is to develop and pilot test a text messaging intervention to increase HPV vaccination in young MSM. The proposed intervention combines an evidence-based approach to increasing vaccination (?reminder-recall?) with text messaging. In addition to providing basic education and a cue to action, text messages can be tailored to address specific barriers. The long-term goal of this research is to develop effective strategies for increasing HPV vaccination among MSM, thereby reducing morbidity, mortality, and disparities associated with HPV-related cancers. In response to PA- 15-263 (The Health of Sexual and Gender Minority Populations), the objective of this R21 application is to develop and pilot test a text messaging intervention to increase HPV vaccination in young adult MSM. Guided by the Information, Motivation, and Behavioral Skills (IMB) Model, we propose to two specific aims: (1) Develop, iteratively refine, and pre-test messages using a 5-step formative research procedure. Intended users of the program (i.e., men who identify as gay, bisexual, or queer 18-26 years old) will be recruited to assist with this process. (2) Test the feasibility, acceptability, and preliminary efficacy of the Txt4Prevention (T4P) text messaging intervention in a pilot randomized controlled trial (RCT). Participants will be randomized to the treatment (T4P) or control condition. The treatment condition will receive a culturally appropriate HPV vaccination intervention based on the IMB model, whereas the control condition will receive a general sexual health intervention that includes basic facts about HPV vaccination readily accessible online. Primary outcome measures include intervention feasibility (recruitment and retention), acceptability (satisfaction with the intervention), and preliminary efficacy as determined by initiation and completion of the 3-dose series at the end of the 9-month trial. Vaccination status will be verified by participants' medical records and the Illinois Immunization Registry. Outcomes from these aims are expected to have an important positive impact by identifying effective strategies for increasing HPV vaccination among sexual minority men.